[MM-45991] Check and return JSON errors (#20735)

model/preference.go

@@ -91,23 +91,21 @@ func (o *Preference) IsValid() *AppError {
 	if o.Category == PreferenceCategoryTheme {
 		var unused map[string]string
 		if err := json.NewDecoder(strings.NewReader(o.Value)).Decode(&unused); err != nil {
-			return NewAppError("Preference.IsValid", "model.preference.is_valid.theme.app_error", nil, "value="+o.Value, http.StatusBadRequest)
+			return NewAppError("Preference.IsValid", "model.preference.is_valid.theme.app_error", nil, "value="+o.Value, http.StatusBadRequest).Wrap(err)
 		}
 	}
 
 	return nil
 }
 
+var preUpdateColorPattern = regexp.MustCompile(`^#[0-9a-fA-F]{3}([0-9a-fA-F]{3})?$`)
+
 func (o *Preference) PreUpdate() {
 	if o.Category == PreferenceCategoryTheme {
 		// decode the value of theme (a map of strings to string) and eliminate any invalid values
 		var props map[string]string
-		if err := json.NewDecoder(strings.NewReader(o.Value)).Decode(&props); err != nil {
-			// just continue, the invalid preference value should get caught by IsValid before saving
-			return
-		}
-
-		colorPattern := regexp.MustCompile(`^#[0-9a-fA-F]{3}([0-9a-fA-F]{3})?$`)
+		// just continue, the invalid preference value should get caught by IsValid before saving
+		json.NewDecoder(strings.NewReader(o.Value)).Decode(&props)
 
 		// blank out any invalid theme values
 		for name, value := range props {
@@ -115,7 +113,7 @@ func (o *Preference) PreUpdate() {
 				continue
 			}
 
-			if !colorPattern.MatchString(value) {
+			if !preUpdateColorPattern.MatchString(value) {
 				props[name] = "#ffffff"
 			}
 		}